Fixing A P0500 Check Engine Light By Re-Soldering The Instrument Cluster

Summary

For anyone that's interested, this post describes my experience in resolving a P0500 check engine light code on a 2nd Gen Tacoma instrument cluster.


Background Symptoms

I have a 2005 2nd Gen Tacoma V6 Auto 4WD with 315,000mi and it's been showing intermittent check engine light with code P0500 for the last year. P0500 is a failure in the VSS (vehicle speed sensor) signal at the ECM (computer). Driving with a OBDII scan tool hooked up, showing VSS live data, shows intermittent no speed signal. However speedometer works normally when the VSS signal drops out.


How It Works

On the 2nd Gen Tacoma V6 Auto configuration, the vehicle speed sensor originates at the four ABS wheel sensors, is processed through the ABS computer, then sent to the instrument cluster, displayed as speed on the speedometer, and reprocessed / conditioned and sent to the ECM (as well as the cruise control, 4WD module, and inverter if installed).
Wheels -> ABS System -> Instrument Cluster -> ECM


Diagnosis

Since the speedometer displayed normal speeds when the VSS signal to the ECM dropped out, this means that the failure is almost certainly in the instrument cluster, and definitely not in any upstream components. In other words since speedometer worked, that means ABS and the four wheel sensors are OK. The instrument cluster itself needs service.


Potential Fixes

This is not a rare issue on 2nd gen Tacomas, and can lead to much frustration chasing diagnosis. There are a number of shops online that specialize in Tacoma instrument cluster rework (google Tacoma P0500 fix to find them). There is also a bypass workaround described in another TacomaWorld post that shows how to feed the input VSS signal from C9-6 directly to the output C9-19 (see references below). I wanted the cluster fixed and not bypassed, but unfortunately, in six months of searching, I was unable to find out *what* component fails or how these clusters are being reworked in repair shops. I suspected a cold solder joint, since the error code seemed to most frequently appear shortly after starting the truck on cold mornings, as the cab was warming up. Temperature-sensitive failures are often due to poor / cold solder joints.


Evaluating the Cluster

I figured it was worth a shot to try to find the cold solder joint myself. There are videos online that show how to remove the Tacoma instrument cluster -- easy, takes about 10 minutes with minimal tools. There is also a video online that shows how to disassemble the 2nd Gen Tacoma instrument cluster (with the purpose of replacing the LEDs). I figured I could learn SMD soldering and rework in about the time (and with similar expense) as it would take to send the cluster off to a repair shop, and if I couldn't fix it, no big deal at least I learned something.

The Factory Service Manual and some online posts indicate that the VSS signal from the ABS system enters the instrument cluster on pin 6 of connector C9. The processed VSS signal leaves the instrument cluster from pin 19 of connector C9.

VSS Signal Path: ABS System -> Cluster Pin C9-6 -> Signal Conditioning Circuit in Cluster -> Cluster Pin C9-19 -> Engine Computer

Disassembly and inspection of the instrument cluster showed no obvious failed solder joints. Using a microscope, I was able to trace the circuit path from C9-6 to an area just to the left of the speedometer motor, and then trace the circuit path from this area back to the output on connector C9-19. Drawing out the schematic of the components in this area revealed two transistors that are likely doing the signal reconditioning, as well as a bunch of supporting resistors, capacitors, and diodes. See photos below. Likely if there was a cold solder joint, it was going to be on one of these components.


Learning SMD Soldering

It took a few evenings to learn SMD (surface-mount device) soldering -- an essential skill for reworking the cluster as the components are very tiny and I didn't want to make things any worse. Using 0.3mm 63/37 solder, flux paste, a temp controlled soldering iron at 350C, and a microscope, I used a SMD practice kit to get comfortable with installing, removing, and reworking SMD devices. 99.9% isopropyl alcohol was used for cleaning. There are plenty of youtube videos that show SMD soldering techniques.


The Fix

After I felt comfortable reworking SMD devices, I re-soldered all of the connections in the areas involved in the VSS signal processing, then cleaned with isopropyl alcohol. See the photos further down for the area of the board and the parts that I specifically reworked, marked in yellow and red. Reassembly of the instrument cluster and reinstallation is fairly straightforward. The issue now seems to be fixed - rather than setting the check engine light every second trip or so, the Tacoma has now been driven 400 miles on > 50 restarts with no signal dropouts.


Conclusion

For this particular set of symptoms - an intermittent P0500 error code with a working speedometer - there's a chance that the issue is due to a cold solder connection on the instrument cluster. Reworking the SMD solder connections on the part of the cluster involved in speed signal processing can be a quick fix to the issue.

Maybe this info can help someone else -- I know TacomaWorld has helped me in the past as a source of really great and hard to find information.



Parts and Supplies:

SMD Soldering Practice Kit

$9 Gikfun DIY SMD SMT Welding Practice Soldering Skill Training Board Ek7028

https://www.amazon.com/dp/B00VWB8F8K?ref=ppx_yo2ov_dt_b_fed_asin_title

MG Chemicals 8341 Flux Paste

$30 MG Chemicals - 8341-10ML 8341 No Clean Flux Paste, 10 milliliters Pneumatic Dispenser (Complete with Plunger & Dispensing Tip)

https://www.amazon.com/dp/B00425FUW2?ref=ppx_yo2ov_dt_b_fed_asin_title

MG Chemicals 824 Isopropyl Alcohol 99.9%

$19 MG Chemicals - 824-1L 99.9% Isopropyl Alcohol Electronics Cleaner, 945 mL (1 Quart) Liquid Bottle

https://www.amazon.com/dp/B005DNQX3C?th=1

0.3mm 63/37 Rosin Core Solder

$9 HengTianMei 63/37 Rosin Core Tin Lead Solder Wire For Electrical Soldering(0.3mm/50g)

https://www.amazon.com/dp/B08M5XDKFG?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

Temp Control Soldering Iron Kit

$60 FNIRSI Soldering Iron Kit, DC/PD(96W/65W) Mini Digital Soldering Iron, 180-780℉ Fast Heating, 6 Soldering Tips, Digital OLED Screen Display, Auto Sleep (With Power Adapter)

https://www.amazon.com/dp/B0C1G9MNNT?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

7" Digital Microscope

$90 7'' Digital Microscope 1200X,Dcorn 12MP 1080P Photo/Video Microscope for Adults Soldering Coins,Metal Stand,Wired Remote,10 LED Fill Lights,PC View,Windows/Mac Compatible

https://www.amazon.com/Microscope-Dcorn-Magnification-Soldering-Compatible/dp/B08K7FGY9Q

Digital Microscope Arm Stand
https://www.amazon.com/dp/B0C1G9MNNT?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

OBDII Scan Tool for Simple VSS Display

$60 ANCEL BD310 OBD2 Scanner & Engine Code Reader - Advanced Battery Test, Trip Analysis, Performance Test, Bluetooth Diagnostic Tool for Android & iPhone - Works for All 1996+ Vehicles

https://www.amazon.com/dp/B07J51W9NS



Helpful References:

2nd Gen Tacoma Instrument Cluster Removal
https://www.youtube.com/watch?app=desktop&v=Tr6tG8VFVlM

2nd Gen Tacoma Instrument Cluster Disassembly
Video for cluster disassembly: https://www.youtube.com/watch?v=VyEDHtdHx2M&t=334s

Clearing P0500 Fault With C9-6 to C9-19 Bypass
https://www.tacomaworld.com/threads/clear-a-single-code-to-pass-inspection.802680/


Photos:

(instrument cluster)
(microscope workstation)
(my crude schematic)
(backside of the cluster showing SMD devices)
(one part of the cluster that needed rework)
(the other part that needed rework)

 

Excellent information, I'll add a link to this in my writeup on the P0500 that can be found here.
https://www.tacomaworld.com/threads/2nd-gen-information-diagnostics.784008/#post-28042157

My suspicion was that it was a solder joint issue but this is the first one I've seen confirmed and repaired, we were just recommending bypassing them since the signal in and signal out is the same by cutting the wire at C9 Pin 19 and connecting it to C9 Pin 6.

Clear a single code to pass inspection | Tacoma World

 

Thanks DM93! Yeah thanks so much for that writeup on the C9-6 to C9-19 bypass. Knowing that the bypass was possible gave me the confidence to try the rework, since if it didn't help, I'd just end up using your bypass instead.

The oscilloscope graph above was a big help too. I also had a 'scope hooked up to the C9-19 speed output from the cluster (referenced to ground), and drove around with it like that for a few weeks. I could totally see when the signal would fail (usually on a cold morning) as the signal would go "high" and stay there. A few minutes later it was back to the normal square wave, presumably as the solder joint came back together. Of course by then the CEL had tripped with the P0500 again.

One curious thing -- I was seeing a +5V square wave on the cluster output to the ECM, but looks like you were seeing a +12V square wave. Maybe there are some differences in models out there.


I appreciate you guys!

 

Welcome!!
Awesome and helpful first post!

 

It seems to depend on which modules are equipped, some modules output a 5v signal and some output a 12v signal, seems to be an average of whats on the SPD circuit. I stated in my post that voltage on the SPD circuit may vary.

 

Great post! Any tips for pulling and reinstalling the needles?

 

Thanks!! Yeah that second video in my references in first post was a big help with the needles. Take a photo of the cluster and needles first. Then use a plastic knife to help pry the needles straight up and off. To put back on, I put them on gently about mid way in their travel, then rotated them to their final position matching the original picture I took. Once in position I pushed a bit further straight down to get them to stick in that position. It was pretty easy and they aligned just fine.

 

Link added.

 

@Orange Dave
First of... bang up job on this post. Absolutely thankful I found this! Thank you thank you.

I have done some solder/PCB work and even done and SMD rework. I brushed up on the rework tutorial videos to refresh my memory too, so I feel confident to attempt this repair.

I have the cluster out and PCB extract. Question:

1. On the pictures you provided, you identified all the components that need rework. But I wondered if on initial inspection, did you notice any components that were obviously suspect? On my own closer inspection... none of the components look suspect. I happen to have a macro lens attachment for my phone so I was able to take a close up. See attached for an example - that's a few of the components you ID'd.

2. On each of the components... did you actually have to remove the component, clean up the pads, add new solder to the pads, and reinstall the component?

or

3. Did you just reheat each pad to reseat the component?

@Dm93
Lastly... I jumped right into assume my issue was the cluster also. Based on eveyrthing I read and the symptoms I am having, I didn't think I needed to bother with the replacing speed sensor to come to the same conclusion that mine is also the cluster:

- 2006 V6 w/ 215K Miles
- P0500 occurs intermittently. It will clear itself most times. Other times, I'll clear and will stay cleared and and then suddenly pop back on
- CEL, VSC, Traction Control, etc all light ups, but only P0500 is stored
- Speedometer has never stopped working

I only have a ScanGauge II, so I'm limited to testing.

With those symptoms, do I need to pause (before I start the PCB rework) and make sure it is the cluster issue (not sending signal to the ECM)?

 

I mean I've yet to see it be anything other than the cluster when the speedometer works all the time but the P0500 sets, 05 and 06 clusters seem to have alot of issues from the p0500 which is most common to one or more gauges not working correctly.
Your already that far so wouldn't hurt to re-flow the solder joints anyway.

 

The components that needs reflowing (as Dave pointed out) are just so darn tiny - I mean tiny!
I've a microscope ordered as well as some other supplies to do a thorough reflow job, but darn it if I'm not nervous about screwing something else up on the board.

I read the bit about jumping C9 Pin 6 and Pin 19. That seems a lot more straightforward. Any chance bypassing the circuitry on the cluster could screw up the ECM (in the long term)?

 

I don't see why, it's just pulsing the circuit to ground just like the cluster would.

 

Hey thanks for the nice comments! I was really hoping this post would help some folks out. Based on your symptoms -- especially that the speedometer works fine while the code is set and the CEL comes on -- the actual sensors and upstream systems are working fine, it's just an issue between the cluster and the computer ... and it seems by far the issue is caused by the cluster itself. Since you've already had the cluster out, the rest is easy at this point.

As for your question -- I looked closely at all of those components (that I identified as part of the speed signal processing circuit by tracing the schematic), and didn't see any of them with an obvious cold solder joint or heat damage or corrosion. Maybe ... just maybe ... the 3-pin transistor or MOSFET with the label as "DF QR" had a very faintly visible crack in the solder joint. I didn't remove any of the components nor cleaned the pads -- I just applied flux, re-heated / reflowed the solder by touching the tip to the solder connection until it reliquified, then cleaned up the flux afterwards with a Q-tip and pure isopropyl alcohol. Super simple and easy, but for sure it helped doing some practice SMD boards first so I was comfortable resoldering the connections under the microscope.

For what it's worth, it's been over three months now without a single code set -- before resoldering those components, it was setting a code every second trip.

I also like the idea others have posted about jumping the pins in C9. If the reflow didn't solve the problem that was going to be my next thing to try.

Let us know how your fix, whichever path you go, works out!

Dave

 

Thank you so much guys !! Really appreciate it! For all the info .

 

@Orange Dave ... well I did it. It's been more than a few days and still no P0500. It normally would have popped up again by now, but has not.

For everyone reading this... just follow everything Dave said in his post. I just wanted to add my key takeaways from this experience in case it helps someone else.

I already had a full solder/rework station from a previous project (

$59 TXINLEI 8586 110V Solder Station, 2 in 1 Digital Display SMD Hot Air Rework Station and Soldering Iron, 12pcs Different Soldering Tips, Tweezers,Desoldering Pump,700W 480℃

https://www.amazon.com/dp/B07FJ6PNHF), but if you don't then just make sure you get a solid one. The one I had worked really well and came with an assortment of tips, including the size to get this done.

If you're a novice, it helps to watch videos like this to get a quick tutorial: https://youtu.be/fYInlAmPnGo?si=0hZe42u2MLpfgTRK. And definitely get the practice board (like Dave suggested). I got one and it helped a lot and allows you to learn from your mistakes before doing it on the real thing. In fact, in the first attempt, the practice board didn't work like it was supposed to. But that was actually a good thing, since that gave me an opportunity to reflow each component. And finally I got it to work right... which gave me more confidence.

As far as those practice boards... they don't come with the best instruction. The PCB components aren't label at all! So it took me a while to sort it out, but finally I realized each component had exactly the same amount the board needed. And the different sizes also help know which component goes where. You just have to know what a Resistor looks like from a Capacitor ... and so when they have the same amount and size, you know which goes where. On the PCB, the locations are labeled with "R" and "C". Watch out for the 4 diodes vs the LEDs (which both are labelled "D" on the board). LEDs are also diodes, which is why their location also gets a D label. There are youtube videos on this practice board (gikfun), which is what helped me get my bearing on this particular product.

You will definitely need a digital microscope. And I recommend getting one with a flexible arm stand, like this one (

$80 Andonstar AD115 Handheld Digital Microscope with 5" Screen for Adults Kids, Portable Coin Microscope for Error Coins with Light, Flexible Boom Arm Stand for Electronics Soldering, Windows Mac

https://www.amazon.com/dp/B0DRYSHCBK)... vs the kind with a built-in stand (like in the link Dave posted above). The others with a built-in base would be fine for small PCBs like the practice borda, but is awkward for larger PCBs like the cluster.

Lastly... take your time prepping for this job. It probably took me 3-4 days waiting for the right tools and supplies I ordered. And then 3-4 hours sorting out the practice board and actually being able to practice on it. But the actual reflow repair took less than 10min. I'm sure the practice helped make sure it all went very smoothly. I've very glad I did.

Apart from that... just follow Dave's guide. It worked flawlessly. Thanks again to @Orange Dave for tracing this down to the T... and then doing the write-up to help a brother out!

 

Hey this is so awesome!! I'm so glad to hear that the fix worked for you too, and it was great reading your write-up of how it worked out! Congrats!!!!!! -Dave

(this forum here has helped me so much, it's nice to see that I was able to give back a little - thanks for posting!)

 

@Orange Dave @Dm93 @dbbyleo are any of you near Fort Wayne Indiana? I am in serious need of help with this as I do not know how to do the things you've done but my Truck seriously needs it ASAP- all the places I have called want 160.00 to 180.00 just to run a diagnostic and that will not go to the repair, and winter is coming fast! I am at my wits end and cannot afford to lose my truck or pay added money for diagnostic and not the repair- I NEED HELP PLEASE!!!

 

Yeah I'm in California so can't help direct. If you can diagnose problem to the P0500 error code coming on as the speedometer is reading normally, that can rule out a wheel sensor or ABS system issue and is almost always the instrument cluster at that point. Before I fixed mine I was going to send it to Tanin Automotive, they do mail-in repair, just google Tanin P0500 Tacoma and you'll find them, there are plenty of other mail-in repair places too.

 

Sorry @Bugz70 ... I'm in Colorado. But like Dave said... there's plenty of outfit that will allow you to mail in your cluster. Places like Tanin has videos on YouTube showing you how exactly to remove the cluster. I believe the link is above in this thread too. Good luck!

 

Well I found a guy that solely does instrument clusters and he would be able to redo mine for 185.00 plus tax so I am SUPER HAPPY- Hopefully that is going to solve my issue but from reading all your posts it seems to be the same issue. Thank you for your feedback.